95 mazda protege reading check engine codes, help please.

I have a 95 Mazda Protege which does not have the OBDII connector, but
the older OBDI connector. I'm told these were the transition year, so
I'm hoping that may be the source of my problem. The check engine
light came on after I replaced the broken down pipe (piece between the
manifold and cat) where the o2 sensor is located. I have a manual that
says for 94 and older that the codes can be flashed out on the check
engine light by placing a jumper between the TEN and GND pins on the
diagnosis connector and turning on the switch to count the flashes. I
have done this, but no flashes are given by the check engine light. I
cleared the codes as described in the manual, check engine light went
out temporarily but then came back on while driving. I suspect that it
may be the o2 sensor, 160K miles and has not been changed, but I would
like to be able to read these codes out before I start shelling out
cash. Does anyone know the method to get these codes to read out?